checkRouteFromStep method
Checks a RouteState at a relative position from the current
one without performing navigation. The step determines
the direction and distance (e.g., -1 for the previous route,1 for the next).
Returns the result of the checker or
Implementation
bool checkRouteFromStep(
int step,
bool Function(RouteState routeState) checker,
) {
final index = pNavigationState.getValue().index + step;
return checkRouteFromIndex(index, checker);
}